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<topic id="overview">
   <title>Overview</title>
   <body>
      <p>The <codeph>gpperfmon</codeph> database consists of three sets of tables;
            <codeph>now</codeph> tables store data on current system metrics such as active queries,
            <codeph>history</codeph> tables store data on historical metrics, and
            <codeph>tail</codeph> tables are for data in transition. <codeph>Tail</codeph> tables
         are for internal use only and should not be queried by users. The <codeph>now</codeph> and
            <codeph>tail</codeph> data are stored as text files on the master host file system, and
         accessed by the <codeph>gpperfmon</codeph> database via external tables. The
            <codeph>history</codeph> tables are regular database tables stored within the
            <codeph>gpperfmon</codeph> database.</p>
      <p>The database consists of three sets of tables:</p>
      <ul>
         <li>
            <codeph>now</codeph> tables store data on current system metrics such as active
            queries.</li>
         <li>
            <codeph>history</codeph> tables store data historical metrics.</li>
         <li>
            <codeph>tail</codeph> tables are for data in transition. These tables are for internal
            use only and should not be queried by end users.</li>
      </ul>
      <p>There are the following categories of tables:</p>
      <ul>
         <li>The <codeph>database_*</codeph> tables store query workload information for a Greenplum
            Database instance.</li>
         <li>The <codeph>diskspace_*</codeph> tables store diskspace metrics.</li>
         <li>The <codeph>interface_stats_*</codeph> tables store statistical metrics for each active
            interface of a Greenplum Database instance. Note: These tables are in place for future
            use and are not currently populated.</li>
         <li>The <codeph>log_alert_*</codeph> tables store information about pg_log errors and
            warnings.</li>
         <li>The <codeph>queries_*</codeph> tables store high-level query status information.</li>
         <li>The <codeph>segment_*</codeph> tables store memory allocation statistics for the
            Greenplum Database segment instances.</li>
         <li>The <codeph>socket_stats_*</codeph> tables store statistical metrics about socket usage
            for a Greenplum Database instance. Note: These tables are in place for future use and
            are not currently populated.</li>
         <li>The <codeph>system_*</codeph> tables store system utilization metrics.</li>
      </ul>
      <p>The <codeph>gpperfmon</codeph> database also contains the following views:</p>
      <ul>
         <li>The <codeph>dynamic_memory_info</codeph> view shows an aggregate of all the segments
            per host and the amount of dynamic memory used per host.</li>
         <li>The <codeph>memory_info</codeph> view shows per-host memory information from the
               <codeph>system_history</codeph> and <codeph>segment_history</codeph> tables.</li>
      </ul>
   </body>
</topic>
